Microalgae are one of the biological energy sources that have the potential to be developed. Microalgal lipids are sealed in cells and can be secreted from the cells by applying the developing gene and metabolic engineering technologies. In addition, it is feasible to rupture the cell wall of the microalgae and extract the lipids from the microalgae. Whether the microalgae can be the mainstream alternative energy source rests in the possibility of improving the extraction efficiency and the performance of extracting the lipids from the microalgae.
Extraction of the lipids from the microalgae is one of the liquid-solid extraction techniques and is achieved by means of a solvent. However, the solid microalgae are small, and after the cell walls of the microalgae are ruptured is 50 by weight at least. Hence, the solvent (e.g., hexane) that is not apt to be dissolved in the water is applied for liquid-solid extraction. On the other hand, when the solvent (e.g., methanol) having the similar polarity to that of the water is utilized for liquid-solid extraction, the solvent needs to be at least twice the microalgae, and thus the costs on separation of the solvent from the microalgae are rather high.